Refactor: drive discovery into platform files, no inline cfg

- drive/unix.rs: find_drives() + resolve_device() for Linux/macOS
- drive/windows.rs: find_drives() + resolve_device() + normalize_path() for Windows
- drive/mod.rs: clean delegation, no cfg branches
- scsi/windows.rs: SPTI transport only, no drive discovery

src/drive/unix.rs

@@ -0,0 +1,52 @@
+//! Unix (Linux/macOS) drive discovery and device resolution.
+
+use crate::error::{Error, Result};
+use crate::identity::DriveId;
+
+pub fn find_drives() -> Vec<(String, DriveId)> {
+    let mut drives = Vec::new();
+    for i in 0..16 {
+        let path = format!("/dev/sg{}", i);
+        if !std::path::Path::new(&path).exists() { continue; }
+        if let Ok(mut transport) = crate::scsi::open(std::path::Path::new(&path)) {
+            if let Ok(id) = DriveId::from_drive(transport.as_mut()) {
+                if !id.raw_inquiry.is_empty() && (id.raw_inquiry[0] & 0x1F) == 0x05 {
+                    drives.push((path, id));
+                }
+            }
+        }
+    }
+    drives
+}
+
+pub fn resolve_device(path: &str) -> Result<(String, Option<String>)> {
+    if path.contains("/sg") {
+        if !std::path::Path::new(path).exists() {
+            return Err(Error::DeviceNotFound { path: path.to_string() });
+        }
+        return Ok((path.to_string(), None));
+    }
+    if path.contains("/sr") {
+        let mut sr_transport = crate::scsi::open(std::path::Path::new(path))?;
+        let sr_id = DriveId::from_drive(sr_transport.as_mut())?;
+        drop(sr_transport);
+        for (sg_path, sg_id) in find_drives() {
+            if sg_id.vendor_id == sr_id.vendor_id
+                && sg_id.product_id == sr_id.product_id
+                && sg_id.serial_number == sr_id.serial_number
+            {
+                let warning = format!(
+                    "{} is a block device (sr) — using {} (sg) for raw access", path, sg_path
+                );
+                return Ok((sg_path, Some(warning)));
+            }
+        }
+        return Ok((path.to_string(), Some(format!(
+            "{} is a block device (sr) — no matching sg device found", path
+        ))));
+    }
+    if !std::path::Path::new(path).exists() {
+        return Err(Error::DeviceNotFound { path: path.to_string() });
+    }
+    Ok((path.to_string(), None))
+}